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Don't use dependent AbortSignals for Subscriber (#154)
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@domfarolino
domfarolino authored Jul 13, 2024
1 parent b8ee44b commit f954c91
Showing 1 changed file with 66 additions and 89 deletions.
155 changes: 66 additions & 89 deletions spec.bs
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Original file line number Diff line number Diff line change
Expand Up @@ -36,7 +36,7 @@ urlPrefix: https://dom.spec.whatwg.org; spec: DOM
text: signal; url: event-listener-signal
for: AbortSignal
text: dependent signals; url: abortsignal-dependent-signals
text: signal abort
text: signal abort; url:abortsignal-signal-abort
</pre>

<style>
Expand Down Expand Up @@ -175,15 +175,9 @@ observer/complete steps=].
Each {{Subscriber}} has a <dfn for=Subscriber>teardown callbacks</dfn>, which is a [=list=] of
{{VoidFunction}}s, initially empty.

Each {{Subscriber}} has a <dfn for=Subscriber>complete or error controller</dfn>, which is an
Each {{Subscriber}} has a <dfn for=Subscriber>subscription controller</dfn>, which is an
{{AbortController}}.

Each {{Subscriber}} has a <dfn for=Subscriber>signal</dfn>, which is an {{AbortSignal}}.

Note: This is a [=create a dependent abort signal|dependent signal=], derived from both
[=Subscriber/complete or error controller=]'s [=AbortController/signal=], and
{{SubscribeOptions}}'s {{SubscribeOptions/signal}} (if non-null).

Each {{Subscriber}} has a <dfn for=Subscriber>active</dfn> boolean, initially true.

Note: This is a bookkeeping variable to ensure that a {{Subscriber}} never calls any of the
Expand All @@ -193,7 +187,7 @@ The <dfn attribute for=Subscriber><code>active</code></dfn> getter steps are to
[=Subscriber/active=] boolean.

The <dfn attribute for=Subscriber><code>signal</code></dfn> getter steps are to return [=this=]'s
[=Subscriber/signal=].
[=Subscriber/subscription controller=]'s [=AbortController/signal=].

<div algorithm>
The <dfn for=Subscriber method><code>next(|value|)</code></dfn> method steps are:
Expand Down Expand Up @@ -228,8 +222,6 @@ The <dfn attribute for=Subscriber><code>signal</code></dfn> getter steps are to

1. [=close a subscription|Close=] [=this=].

1. [=AbortController/Signal abort=] [=this=]'s [=Subscriber/complete or error controller=].

1. Run [=this=]'s [=Subscriber/error algorithm=] given |error|.

[=Assert=]: No <a spec=webidl lt="an exception was thrown">exception was thrown</a>.
Expand All @@ -247,8 +239,6 @@ The <dfn attribute for=Subscriber><code>signal</code></dfn> getter steps are to

1. [=close a subscription|Close=] [=this=].

1. [=AbortController/Signal abort=] [=this=]'s [=Subscriber/complete or error controller=].

1. Run [=this=]'s [=Subscriber/complete algorithm=].

[=Assert=]: No <a spec=webidl lt="an exception was thrown">exception was thrown</a>.
Expand All @@ -274,43 +264,51 @@ The <dfn attribute for=Subscriber><code>signal</code></dfn> getter steps are to
<div algorithm>
To <dfn>close a subscription</dfn> given a {{Subscriber}} |subscriber|, run these steps:

1. Set |subscriber|'s [=Subscriber/active=] boolean to false.
1. If |subscriber|'s [=Subscriber/active=] is false, then return.

<div class=note>
<p>This algorithm intentionally does not have script-running side-effects; it just updates the
internal state of a {{Subscriber}}. It's important that this algorithm sets
[=Subscriber/active=] to false and clears all of the callback algorithms *before* running any
script, because running script <span class=allow-2119>may</span> reentrantly invoke one of the
methods that closed the subscription in the first place. And closing the subscription <span
class=allow-2119>must</span> ensure that even if a method gets reentrantly invoked, none of the
{{SubscriptionObserver}} callbacks are ever invoked again. Consider this example:</p>

<div class=example id=reentrant-example>
<pre highlight=js>
let innerSubscriber = null;
const producedValues = [];

const controller = new AbortController();
<div class=note>
<p>This guards against re-entrant invocation, which can happen in the "producer-initiated"
unsubscription case. Consider the following example:</p>
<div class=example id=re-entrant-close>
<pre highlight=js>
const outerController = new AbortController();
const observable = new Observable(subscriber =&gt; {
innerSubscriber = subscriber;
subscriber.addTeardown(() =&gt; {
// 2.) This teardown executes inside the "Close" algorithm, while it's
// running. Aborting the downstream signal run its abort algorithms,
// one of which is the currently-running "Close" algorithm.
outerController.abort();
});

// 1.) This immediately invokes the "Close" algorithm, which
// sets subscriber.active to false.
subscriber.complete();
});

observable.subscribe({
next: v =&gt; producedValues.push(v),
complete: () =&gt; innerSubscriber.next('from complete'),

}, {signal: controller.signal}
);

// This invokes the complete() callback, and even though it invokes next() from
// within, the given next() callback will never run, because the subscription
// has already been "closed" before the complete() callback actually executes.
controller.abort();
console.assert(producedValues.length === 0);
</pre>
</div>
</div>
observable.subscribe({}, {signal: outerController.signal});
</pre>
</div>
</div>

1. Set |subscriber|'s [=Subscriber/active=] boolean to false.

1. [=AbortSignal/Signal abort=] |subscriber|'s [=Subscriber/subscription controller=].

Issue: Abort with an appropriate abort reason.

1. [=list/For each=] |teardown| of |subscriber|'s [=Subscriber/teardown callbacks=] sorted in
reverse insertion order:

1. If |subscriber|'s [=relevant global object=] is a {{Window}} object, and its [=associated
Document=] is not [=Document/fully active=], then abort these steps.

Note: This step runs repeatedly because each |teardown| could result in the above
{{Document}} becoming inactive.

1. [=Invoke=] |teardown|.

If <a spec=webidl lt="an exception was thrown">an exception |E| was thrown</a>, call
|subscriber|'s {{Subscriber/error()}} method with |E|.
</div>

<h3 id=observable-api>The {{Observable}} interface</h3>
Expand Down Expand Up @@ -526,37 +524,16 @@ An <dfn>internal observer</dfn> is a [=struct=] with the following [=struct/item
: [=Subscriber/complete algorithm=]
:: |internal observer|'s [=internal observer/complete steps=]

: [=Subscriber/signal=]
:: The result of [=creating a dependent abort signal=] from the list «|subscriber|'s
[=Subscriber/complete or error controller=]'s [=AbortController/signal=], |options|'s
{{SubscribeOptions/signal}} if it is non-null», using {{AbortSignal}}, and the [=current
realm=].

1. If |subscriber|'s [=Subscriber/signal=] is [=AbortSignal/aborted=], then [=close a
subscription|close=] |subscriber|.
1. If |options|'s {{SubscribeOptions/signal}} [=map/exists=], then:

Note: This can happen when {{SubscribeOptions}}'s {{SubscribeOptions/signal}} is already
[=AbortSignal/aborted=].
1. If |options|'s {{SubscribeOptions/signal}} is [=AbortSignal/aborted=], then [=close a
subscription|close=] |subscriber|.

1. Otherwise, [=AbortSignal/add|add the following abort algorithm=] to |subscriber|'s
[=Subscriber/signal=]:
1. Otherwise, [=AbortSignal/add|add the following abort algorithm=] to |options|'s
{{SubscribeOptions/signal}}:

1. [=close a subscription|Close=] |subscriber|.

1. [=list/For each=] |teardown| of |subscriber|'s [=Subscriber/teardown callbacks=] sorted in
reverse insertion order:

1. If |subscriber|'s [=relevant global object=] is a {{Window}} object, and its
[=associated Document=] is not [=Document/fully active=], then abort these steps.

Note: This step runs repeatedly because each |teardown| could result in the above
{{Document}} becoming inactive.

1. [=Invoke=] |teardown|.

If <a spec=webidl lt="an exception was thrown">an exception |E| was thrown</a>, call
|subscriber|'s {{Subscriber/error()}} method with |E|.

1. If [=this=]'s [=Observable/subscribe callback=] is a {{SubscribeCallback}}, [=invoke=] it
with |subscriber|.

Expand Down Expand Up @@ -618,9 +595,9 @@ For now, see [https://github.com/wicg/observable#operators](https://github.com/w

Note: This will "unsubscribe" from |sourceObservable|, if it has been subscribed to by
this point. This is because |sourceObservable| is subscribed to with the "outer"
|subscriber|'s [=Subscriber/signal=] as an input signal, and that signal will get
[=AbortSignal/signal abort|aborted=] when the "outer" |subscriber|'s
{{Subscriber/complete()}} is called above (and below).
|subscriber|'s [=Subscriber/subscription controller=]'s [=AbortController/signal=] as
an input signal, and that signal will get [=AbortSignal/signal abort|aborted=] when the
"outer" |subscriber|'s {{Subscriber/complete()}} is called above (and below).

: [=internal observer/error steps=]
:: Run |subscriber|'s {{Subscriber/complete()}} method.
Expand All @@ -631,7 +608,7 @@ For now, see [https://github.com/wicg/observable#operators](https://github.com/w
mirror |sourceObservable| uninterrupted.

1. Let |options| be a new {{SubscribeOptions}} whose {{SubscribeOptions/signal}} is
|subscriber|'s [=Subscriber/signal=].
|subscriber|'s [=Subscriber/subscription controller=]'s [=AbortController/signal=].

1. <a for=Observable lt="subscribe to an Observable">Subscribe</a> to |notifier| given
|notifierObserver| and |options|.
Expand Down Expand Up @@ -705,7 +682,7 @@ For now, see [https://github.com/wicg/observable#operators](https://github.com/w
:: Run |subscriber|'s {{Subscriber/complete()}} method.

1. Let |options| be a new {{SubscribeOptions}} whose {{SubscribeOptions/signal}} is
|subscriber|'s [=Subscriber/signal=].
|subscriber|'s [=Subscriber/subscription controller=]'s [=AbortController/signal=].

1. <a for=Observable lt="subscribe to an Observable">Subscribe</a> to |sourceObservable|
given |sourceObserver| and |options|.
Expand Down Expand Up @@ -751,7 +728,7 @@ For now, see [https://github.com/wicg/observable#operators](https://github.com/w
:: Run |subscriber|'s {{Subscriber/complete()}} method.

1. Let |options| be a new {{SubscribeOptions}} whose {{SubscribeOptions/signal}} is
|subscriber|'s [=Subscriber/signal=].
|subscriber|'s [=Subscriber/subscription controller=]'s [=AbortController/signal=].

1. <a for=Observable lt="subscribe to an Observable">Subscribe</a> to |sourceObservable|
given |sourceObserver| and |options|.
Expand Down Expand Up @@ -793,7 +770,7 @@ For now, see [https://github.com/wicg/observable#operators](https://github.com/w
:: Run |subscriber|'s {{Subscriber/complete()}} method.

1. Let |options| be a new {{SubscribeOptions}} whose {{SubscribeOptions/signal}} is
|subscriber|'s [=Subscriber/signal=].
|subscriber|'s [=Subscriber/subscription controller=]'s [=AbortController/signal=].

1. <a for=Observable lt="subscribe to an Observable">Subscribe</a> to |sourceObservable|
given |sourceObserver| and |options|.
Expand Down Expand Up @@ -832,7 +809,7 @@ For now, see [https://github.com/wicg/observable#operators](https://github.com/w
:: Run |subscriber|'s {{Subscriber/complete()}} method.

1. Let |options| be a new {{SubscribeOptions}} whose {{SubscribeOptions/signal}} is
|subscriber|'s [=Subscriber/signal=].
|subscriber|'s [=Subscriber/subscription controller=]'s [=AbortController/signal=].

1. <a for=Observable lt="subscribe to an Observable">Subscribe</a> to |sourceObservable|
given |sourceObserver| and |options|.
Expand Down Expand Up @@ -911,7 +888,7 @@ For now, see [https://github.com/wicg/observable#operators](https://github.com/w
|subscriber|'s {{Subscriber/complete()}} method.

1. Let |options| be a new {{SubscribeOptions}} whose {{SubscribeOptions/signal}} is
|subscriber|'s [=Subscriber/signal=].
|subscriber|'s [=Subscriber/subscription controller=]'s [=AbortController/signal=].

1. <a for=Observable lt="subscribe to an Observable">Subscribe</a> to |sourceObservable|
given |sourceObserver| and |options|.
Expand Down Expand Up @@ -976,7 +953,7 @@ For now, see [https://github.com/wicg/observable#operators](https://github.com/w
had not yet completed. Until right now!

1. Let |innerOptions| be a new {{SubscribeOptions}} whose {{SubscribeOptions/signal}} is
|subscriber|'s [=Subscriber/signal=].
|subscriber|'s [=Subscriber/subscription controller=]'s [=AbortController/signal=].

1. <a for=Observable lt="subscribe to an Observable">Subscribe</a> to |innerObservable| given
|innerObserver| and |innerOptions|.
Expand Down Expand Up @@ -1044,7 +1021,7 @@ For now, see [https://github.com/wicg/observable#operators](https://github.com/w
{{Subscriber/complete()}} method.

1. Let |options| be a new {{SubscribeOptions}} whose {{SubscribeOptions/signal}} is
|subscriber|'s [=Subscriber/signal=].
|subscriber|'s [=Subscriber/subscription controller=]'s [=AbortController/signal=].

1. <a for=Observable lt="subscribe to an Observable">Subscribe</a> to |sourceObservable|
given |sourceObserver| and |options|.
Expand Down Expand Up @@ -1098,7 +1075,8 @@ For now, see [https://github.com/wicg/observable#operators](https://github.com/w
1. Let |innerOptions| be a new {{SubscribeOptions}} whose {{SubscribeOptions/signal}} is the
result of [=creating a dependent abort signal=] from the list
«|activeInnerAbortController|'s [=AbortController/signal=], |subscriber|'s
[=Subscriber/signal=]», using {{AbortSignal}}, and the [=current realm=].
[=Subscriber/subscription controller=]'s [=AbortController/signal=]», using
{{AbortSignal}}, and the [=current realm=].

1. <a for=Observable lt="subscribe to an Observable">Subscribe</a> to |innerObservable| given
|innerObserver| and |innerOptions|.
Expand Down Expand Up @@ -1134,10 +1112,9 @@ For now, see [https://github.com/wicg/observable#operators](https://github.com/w
reason=].

Note: All we have to do here is [=reject=] |p|. Note that the subscription to [=this=]
{{Observable}} will also be canceled automatically, since the "inner"
[=Subscriber/signal=] (created during <a for=Observable lt="subscribe to an
Observable">subscription</a>) is a [=AbortSignal/dependent signal=] of |options|'s
{{SubscribeOptions/signal}}.
{{Observable}} will also be closed automatically, since the "inner" Subscriber gets
[=close a subscription|closed=] in response to |options|'s {{SubscribeOptions/signal}}
getting [=AbortSignal/signal abort=].

1. Let |values| be a new [=list=].

Expand Down Expand Up @@ -1537,8 +1514,8 @@ partial interface EventTarget {
Note: This is meant to capture the fact that |event target| can be garbage collected
by the time this algorithm runs upon subscription.

1. If |subscriber|'s [=Subscriber/signal=] is [=AbortSignal/aborted=], abort these
steps.
1. If |subscriber|'s [=Subscriber/subscription controller=]'s [=AbortController/signal=]
is [=AbortSignal/aborted=], abort these steps.

1. [=Add an event listener=] with |event target| and an [=event listener=] defined as follows:

Expand Down

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